The present invention relates to apparatus and technique for regulating stacked high voltage DC power supplies, e.g., having individual section output voltages in the range of 300 to 1,000 volts DC. More particularly, the invention relates to an invertor circuit for deriving stable, high voltage supplies from unstable reference voltages, with the minimum of weight and complexity.
One application of the present invention concerns towed aircraft decoys incorporating high voltage components, such as traveling wave tubes. Such devices normally require multiple high voltage inputs, only some of which may be directly available from the aircraft voltage distribution system. Signals and high voltage inputs are communicated from the aircraft to the decoy via an extended length tow line. The high voltage inputs are attenuated by the tow line by amounts that correspond to factors such as length of the tow line, the temperature which the tow line is exposed, and other environmental factors. As a result, the voltage levels received by the decoy may vary considerably in response to particular flight conditions. In turn, those variances cause instability in relation to power signals derived from the voltage levels communicated via the tow line. As a result of those variances in the required and derived voltage levels, the efficiency of the decoy invertor circuit is reduced, and output of the traveling wave tube may be degraded.
Contemporary devices have utilized techniques for regulating outputs derived from unstable input sources. One such technique is based on pulse width modulation in response to received signal levels. By modulating the pulse width, the invertor output voltage may be regulated to remain within confined limits. However, pulse width modulation techniques typically require complex circuitry adapted to accommodate pulse width changes within the switching circuitry. While such contemporary techniques are suitable for certain applications, they are less useful in environments where space and complexity limitations favor simple techniques that reliably function in hostile temperature or electronic environments.
The present invention is directed to providing such apparatus and techniques for regulating derived high voltage DC signals, using a simple technique that will reliably operate in a variety of hostile environments.
Although not specific to towed decoy applications, this technology lends itself to operation of high frequency power amplifiers where compact, efficient, and capable power conditioner circuitry is locally installed in a decoy aerobody. A three wire towed decoy topology, for example, provides source voltages of -2000 Vdc, +350 Vdc, and a return line for a remotely located high frequency power conditioner via a small wire gauge tow cable. For such decoy applications, at least two high frequency power amplifiers are required (TWTs), which results in a total input power of over 1400 Watts with full RF drive.
Due to resistive tow cable losses and the resulting power transfer limitations, power requirement for such applications cannot be taken from the +350 Vdc source. The alternate method of providing this power, at the end of the tow cable, is to use the high voltage, -2000 Vdc, as the prime power source for the remote resonant switch mode invertor. Resistance and power transfer limitations will force a split of power from the -2000V source and from the +350 V source.